Rigid Pavement Empirical Design Example

Design a new rigid pavement for a major interstate highway using the following conditions (four lanes each direction):

Design ESALs

The standard multiplier to calculate compound growth is:

Calculate the Effective Modulus of Subgrade Reaction (k) This calculation is a multi-step process In the 1993 AASHTO Guide for Design of Pavement Structures. Basically, the steps are as follows:

1. Determine the roadbed resilient modulus and the subbase elastic modulus and use these values along with a projected slab thickness to graphically determine a "composite modulus of subgrade reaction" (k_:).
2. Modify this k_: to account for the effects of a rigid foundation near the surface. The idea here is that the subgrade will offer greater support if a rigid foundation (such as bedrock) is located very near the surface.
3. Determine how this modified composite modulus of subgrade reaction (or "k-value") varies throughout a typical year. Typically this is done by season or by month.
4. Using a projected slab thickness and a modulus of subgrade reaction that has been modified to account for the effects of a rigid foundation near the surface, use a graph to determine the relative influence the various k-values throughout the year will have on pavement performance. Lower values of k, indicating less support, are potentially more damaging than higher values of k, indicating more support. Therefore, lower values of k are weighted more heavily in determining the weighted average.
5. Correct the weighted average k-value to account for the potential loss of support arising from subbase erosion. Subbase materials that are more prone to eroding will result in a larger downward correction to the k-value determined in step 4.

The 1993 AASHTO Guide for Design of Pavement Structures and its associated graphs are needed to carry out this procedure because most steps involve graphical solutions. Although these graphs are not reproduced here, a summary results table is shown below.

average relative damage

=

Based on Figure 3.5 in the 1993 AASHTO Guide for Design of Pavement Structures, k ˜ 980.

Based on Figure 3.6 in the 1993 AASHTO Guide for Design of Pavement Structures a Loss of Support = 1.0 results in $k_{eff}$ ˜ 250.

Use the 1993 AASHTO Empirical Equation Using the previously calculated ESAL results and the 1993 AASHTO empirical rigid pavement design equation the following pavement thickness designs can be calculated:

In this particular example, which only shows one set of possible solutions, the HMA base course and crushed stone subbase course layer depths were kept constant and the PCC surface course depth was varied depending upon requirements. Notice that a change in reliability level from 90% to 99% results in a PCC slab thickness increase of about 50 mm (2 inches). The 380 mm (15 inch) thick slab shown for the 40-year design (99% reliability) is probably near the maximum practical slab thickness for highway pavements.

Calculator

1993 AASHTO rigid pavement design

1993 AASHTO Guide, Part II §3.2

Finds the PCC slab depth that carries the design traffic at the chosen reliability.

Units

US customary SI (metric)

Traffic and reliability

Design ESALs

Rigid-pavement ESALs in the design lane over the design period.

Reliability50 % (ZR = 0.000)60 % (ZR = −0.253)70 % (ZR = −0.524)75 % (ZR = −0.674)80 % (ZR = −0.841)85 % (ZR = −1.037)90 % (ZR = −1.282)91 % (ZR = −1.340)92 % (ZR = −1.405)93 % (ZR = −1.476)94 % (ZR = −1.555)95 % (ZR = −1.645)96 % (ZR = −1.751)97 % (ZR = −1.881)98 % (ZR = −2.054)99 % (ZR = −2.327)99.9 % (ZR = −3.090)99.99 % (ZR = −3.750)

Overall standard deviation, S₀

Typically 0.30 to 0.40 for rigid pavements.

Serviceability

Initial serviceability, p_i

Terminal serviceability, p_t

Concrete and support

PCC elastic modulus, E_c, psi

PCC modulus of rupture, S′_c, psi

Effective modulus of subgrade reaction, k, pci

Load transfer coefficient, J

3.2 for doweled jointed pavement with asphalt shoulders.

Drainage coefficient, C_d

CalculateExample values: the 1993 Guide’s Figure 3.7 example.

@misc{pavint-rigid-pavement-empirical-design-example,
  author = {{Pavement Interactive}},
  title = {Rigid Pavement Empirical Design Example},
  year = {2018},
  publisher = {HeadLight},
  howpublished = {\url{https://pavementinteractive.org/reference-desk/design/structural-design/rigid-pavement-empirical-design-example/}},
  note = {Accessed [date]}
}